Ball



Patented Jan. 18, 1927.

. UNITED STATES LOUIS SCHWARTZ, NEW YORK, N. Y.

BALL.

Application filed June 5, 1923. Serial No. 643,524.

The object of my invention is to provide an improved tennis ball. The ordinary tennis ball is a hollow, felt or melton covered, rubber ball, the felt covering causing the 6 ball to grip or cling to the strings of the racquet and surface of the court so that cut, topped, and sliced strokes may be achieved. A felt or melton covered ball is not entirely satisfacto for the purpose,

to however, for a number 0 reasons. For example, its initial surface is quickly destroyed by strenuous play so that its grip or cling, and likewise its weight, 1s materially lessened; the felt readily absorbs IIlOlS- Hi ture and as a consequence the ball becomes heavy when played on damp ground; the felt is quickly soiled and cannot be cleaned easily; and under heavy strokes the fabric cover is commonly torn away from the rubher beneath it. This last I believe to be due in large part to the fact that the fabric cover is comparatively non-elastic, while the underlying rubber to which it is cemented is highly elastic and yields freely to every impact. 2 An acceptable tennis ball must not only meet the requirements of accepted specifications (such as those of weight, resiliency,

etc.), but it must also be sufiiciently unyielding to retain its shape, to a certain degree, under heavy blows, and yet must possess at least substantially the same degree of cling as the ordinary felt covered ball. I have found that sponge rubber, in which the cells are small, and which retains the thin skin which is produced on the surface of the sheet as an incident in the formation of the sponge, possesses the degree of cling required of tennis balls. The resilient cellular structure of such a material permits the racquet strings and minute" irregularities-of the surface of the court to penetrate the surface of balls made thereof, and individually embed themselves in the ball. Not only do the racquet strings act as a unit to flatten the ball at impact, but also each string is embedded, individuall well into the resilient cellular structure, or by reason of its combined resiliency and cellular or sponge formation, such a material penetrates between the racquet strings, and by reason of its diminished cohesiveness (as compared to a non-sponge stroke, and responds to the spin as it rebounds from the court. The skin improves the wearing qualities of the sponge rubber, prevents absorption of moisture, is not so readily soiled as felt, and facilitates cleaning. Thesoftness of the spongematerial is excessive, however, so that a ball composed entirely of this material is altogether too soft for the purposes'of tennis balls. Further-- more, a ball of sponge rubber lacks the required tensile strength, and wei ht or resiliency, or both, when made of the size required by the accepted specifications to the game. I therefore construct only the outer portion of the ball of sponge rubber (preferably covered with a thin rubber skin or tread, as described), this surfacing cellularportion being only enough to provide the ball with the desired surface effects or characteristics. vide or complete the remaining characteristics desired, I complement this comparatively thin walled surface structure with an inner and comparatively dense but very resilient vulcanized rubber compound to the extent necessary, that is to say, I employ underneath the sponge a material of which rubber is a constituent and which is of'such a com position, thickness and density as to provide the ball with, or to complete in the ball, those desired characteristics in which the sponge surfacing is deficient. The finished ball therefore is composite in its nature, being cellular at the outer surface and denser underneath. The surface of the composite ball being even more elastic than the underlying To prosubstantially thick layers, there is little or no tendency for the sponge to separate from the core under the stresses of play and heat. Furthermore, the ball may be inflated with a gas under somewhat greater pressure than atmosphere. The denser portion of the ball retains this gas without that undue distention that would be exhibited by sponge. rubber alone. At the same time, the sponge rubber of the composite wall, and likewise the outer skin, vif used, tend to retain for a time, any gas that may pass the denser rubber, so that the life and resiliency of the ball is prolonged.

While the ball of my intention is primarily intended for tennis, itis obvious that it maybe used for other purposes.

r In the* accompanying drawing illustrating my invention:

Figure 1 is a diagrammatic section of a portion of a ball on a rather large scale;

of a tennis ball in which the outer cellular and inner dense portions are initially separate and are joined by cementing or the like;

Figure 3 is a section of the ball of Figure 2 illustrating a detail of the joining of the separate inner and outer layers.

Referring to Figure 1, the ball of my invention as before explained comprises a hollow, usually imprevious, spherical center or core 10, such as is afforded by a suitable dense vulcanized rubber compound, and a resilient cellular surfacing 11 such as 'is provided by a fine sponge rubber, that is to say, a resilient rubber structure of small closely-spaced cells. The desired surface effects or characteristics of the ball are primarily provided by the resiliently cellular surfacing 11 independently of the core 10. This surfacing affords the grip or cling required of tennis balls in the manner before indicated, that is, the great resiliency of the surface permits the strings of the racquet and minute, irregularities of the court surface to sink well into the surface of the ball while the diminished cohesiveness due to the cellularity of the structure embeds the individual strings and court irregularities for the moment that the ball-is in contact. The thickness of the cellular surfacing depends on the surface softness and cling desired of the ball, and also on the cellular structure and the composition of the material. I have found a thickness of fine sponge rubber in the neighborhood of 011esixteenth of an inch (more or less) to be quite satisfactory for the purposes of tennis. If too thick a la er is used, the surface of the ball is too so t for satisfactory play; on the other hand, too thin a surfacing renders the surface too hard and the ball fails to cling sufficiently. The core 10 is resilient like the core of the ordinary felt covered ball and it primarily affords the resiliency and Weight required of the ball (account being taken of the characteristics of the cellular surfacing and of any gas content); its composition and construction are determined by those requirements of the ball which it is adapted to meet primarily. Generally, these include all the requirements of the ball except those relating to the surface.- The core is also intended to primarily retain any compressed gas content. The core 10, it will be observed, therefore, complements the cellular surfacing 11 to whatever extent may be necessary in order for the ball to meet the desires of players and the requirements of specifications. The surfacing 11 may be so chosen therefore and so constructed, as may best fulfill the rules and requirements of the game.

Outside the surfacing 11 the thin skin or tread 12 is preferably employed to improve the Wearing qualities, facilitate Washing,

and render the ball wholly or more thoroughly Waterproof as before pointed out. This tread is quite thin and flexible so that the surfacing 11 may act through it in the man ner indicated. A vulcanized rubber is a suitable material, and the tread may be formed as an incident in the formation of the sponge rubber sub-surface as before indicated; that is to say, in the formation of sheet'sponge rubber a thin rubber skin is or may be left at the surface of the sponge; such a skin is quite suitable for the tread indicated at 12 so that this tread and the sponge sub-surface 11 may readily comprise an integral structure. Also, as before stated, this outer skin or tread and the cellular structure 11 may both assist the core 10 in retaining any compressed-gas content of the ball, that is to say, may themselves for a time retain gas passing the core, so that retention of any such' gas Within the ball is prolonged.

The manner in which the surfacing 11 and the core 10 are united is substantially nonessential. They may be integral parts of the same structure, the unitary material grading for example from the cellular structure on theoutside to the dense material underneath, or they may be separately formed and united by vulcanizing, cementing, etc., either before or after being given their spherical conformation. In the con struction shown in Figs. 2 and 3 the core 10 of dense (non-sponge) vulcanized rubberf compound is first formed complete. From sheets of fine sponge rubber two pieces of like dumb-bell shape are cut for the outer surfacing 11; these dumb-bell pieces have the usual shapes oftWo-piece ball covers as appears from Fig. 2; These pieces of sponge rubbers are then cemented to the core. In this method of construction the sponge sheets may include a thin skin 13 similar to the outer skin 12 and which likewise may be formed as an incident to the formation of the sponge rubber. I believe this inner skin 13 to be preferable where the surfacing is attached to the core in this manner since it provides a larger aggregate area for adhesion to the surface of the core. The core .0 of the completed ball of Figure 2 confines a suitable gas compressed somewhat above atmospheric pressure. As before indicated, the invention isnot limited to this cemented type of construction, however.

Claims- I 1. A tennis ball comprising a surfacing of sponge rubber provided with an outer skin and a resilient hollow spherical core containmg a compressed gas.

2. A tennis ball comprising a hollow sperical core of dense rubber material, said core retaining gas under pressure, and a separatey made sponge rubber surfacing thereon.

3. A tennis ball comprising a hollow spherical ,core of a substantially impervious material, said core retaining a body of gas Within itself, and aspon e rubber surfacing having a skin at each si e, said sponge rub- 5 ber being aflixed to the core material.

4. A tennis ball comprising a hollow spherical, core of a dense rubber material, said core retaining gas under pressure, and a surfacing of sheeted' sponge rubber at- 10 tached thereto.

5. A tennis ball comprising ahollow spherical core of a dense vulcanized rubbero compound adapted to retain a body of gas, and a separately-made thin sponge rubber cover therefonto afford the grip uired, 15 said sponge rubber cover having a t inner substantia 1y imperforate skin to render said cover non-absorptive. In testimony whereof, I have signed this specification.

LOUIS SCHWARTZ. 

